function f = gpr2(x)
if nargin == 1
 x1 = x(1);
 x2 = x(2);
else
 x1 = x;
 x2 = y;
end
f =(1+(x1+x2+1).^2.*(19-14.*x1+3.*x1.^2-14.*x2+6.*x1.*x2+3.*x2.^2))...
.*(30+(2.*x1-3.*x2).^2.*(18-32.*x1+12.*x1.^2+48.*x2-36.*x1.*x2+27.*x2.^2));
